This invention relates to methods for stabilizing organic materials which are prone to deterioration via thermal and/or oxidative mechanisms and to the resulting stabilized materials. More particularly, the invention relates to such methods and compositions which employ methyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate as a stabilizer [also known in alternate nomenclature as methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and identified herein as MBPP].
Methods for the stabilization of polyether polyols and other polymeric materials with antioxidants or other stabilizers and the use of the stabilized polyols in the preparation of polyurethane foams to inhibit scorch are well known. Polyether polyols, used in the manufacture of slabstock flexible and semiflexible polyurethane foams, are typically stabilized with antioxidant packages consisting of phenolic and amine antioxidants which may also contain synergists such as phenothiazine or various compounds containing phosphite moieties.
Polyurethane foams have been conventionally prepared by reacting a high equivalent weight isocyanate-reactive compound and a polyisocyanate in the presence of a blowing agent. Useful blowing agents include, for example, water, low boiling liquids, such as chlorofluorocarbon, methylene chloride and liquid carbon dioxide, or mixtures thereof.
A persisting problem, however, in the preparation of flexible polyurethane foams, especially in slabstock-type foams, is foam polymer degradation resulting in discoloration (herein also referred to as xe2x80x9cscorchxe2x80x9d).
Scorch is a well-known thermo-oxidative process caused by the heat released from the exothermic reactions, especially from the exothermic reaction between water and the isocyanate. This thermo-oxidative process may be further exacerbated by the ambient heat and humidity conditions and can reach levels of self-ignition of the foam. Therefore, scorch is considered one of the most serious issues since it represents a potential fire hazard for the foam manufacturers. Scorch is normally expressed as a function of coloration of the foam which is expressed as delta E. The higher delta E, the higher the scorch of the foam.
While 2,6-di-tert-butyl-4-methyl phenol, also referred to as butylated hydroxytoluene, or BHT has been widely used for many years as a stabilizer for polymers, it is subject to several drawbacks including its relatively high volatility, its ability to sublime and its ability to form highly colored chromophores which can cause discoloration in polymers, polymer foams and materials in contact with the polymers. Accordingly, many investigations have been undertaken to modify the chemistry of BHT to eliminate or mitigate the aforementioned drawbacks or to replace BHT entirely with some other stabilizer of equivalent or superior effectiveness.
In accordance with the present invention, a process for preparing a flexible polyurethane foam comprising reacting together an organic polyisocyanate with an isocyanate-reactive composition, wherein one of the reactants has mixed therewith a stabilizing amount of methyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, in the presence of a blowing agent and under conditions sufficient to form the polyurethane or polyisocyanurate foam. Also disclosed is an isocyanate-reactive composition comprising an isocyanate-reactive compound having an equivalent weight of from about 400 to about 12000, and a stabilizing amount of methyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate. Additionally disclosed is a method for stabilizing an organic material that is subject to thermal and/or oxidative deterioration is provided which comprises incorporating into such material a stabilizing amount of methyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, optionally with another phenolic and/or an amine and/or phosphite or thioether or lactone stabilizer to form a stabilizer package for polyols, polyurethanes and other oxidatively degradeable polymeric materials.